The nervous system is comprised of two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS includes the brain and the spinal cord and controls most functions of the body and mind. The remainder of the nervous system is the PNS. Nerves of the PNS connect the CNS to sensory organs (such as the eyes and ears), other organs of the body, muscles, blood vessels, and glands. The peripheral nerves include the cranial nerves, the spinal nerves, and roots.
The CNS controls all voluntary movement, such as movement of the legs during walking, and all involuntary movement, such as beating of the heart. The spinal cord connects the body and the brain by transmitting information to and from the body and the brain.
The nervous system can be injured in numerous ways, and injuries can be traumatic. For instance, sudden physical assault on a portion of the nervous system results in a traumatic injury. In the case of a traumatic brain injury, the injury can be focal, i.e., confined to a specific area of the brain, or diffuse, i.e., involving more than one area of the brain.
Injuries to the nervous system include contusions, which are bruises of the nervous system, and blood clots. Blood clots can form in or around the nervous system. For example, when bleeding occurs between the skull and the brain, the blood forms a clot. This puts pressure on the brain, which can lead to changes in brain function.
Spinal cord injuries (SCI) are a particular type of injury to the nervous system. As of the year 2000, approximately 450,000 people in the United States have sustained SCI, with more than 10,000 new cases reported in the United States every year. Motor vehicle accidents are the leading cause of SCI (44 percent), followed by acts of violence (24 percent), falls (22 percent), sports injuries (8 percent), and other causes (2 percent). Of the 10,000 new cases of SCI in the United States each year, 51.7% have tetraplegia, i.e., injuries to one of the eight cervical segments of the spinal cord, and 56.7% have paraplegia, i.e., lesions in the thoracic, lumbar, or sacral regions of the spinal cord. Since 1990, the most frequent neurologic category is incomplete tetraplegia (29.5%), followed by complete paraplegia (27.9%), incomplete paraplegia (21.3%), and complete tetraplegia (18.5%).
With spinal cord injuries in the neck, significant impairment of breathing may result. The most frequent site of spinal injury is the neck or cervical region and, of these, the major cause of death arises from respiratory complications. For patients that survive a major spinal cord injury in the neck, they may spend the rest of their lives depending on an artificial ventilator or phrenic nerve pacemaker to sustain their lives. For others with less severe respiratory impairment, they may be able to breathe normally, but are unable to sigh or breathe deeply and maintain the integrity of the lung. As a consequence, regions of the lung will collapse in these patients, causing pneumonia and allowing other respiratory infections to become established. Clearly, restoration of normal breathing ability, including deep breaths and sighs, is a major goal in the treatment of spinal cord injury patients.
Injury to the spinal cord and other parts of the nervous system may be particularly devastating to life and the quality of life. In addition, injury to the nervous system can engender serious economic losses to the individual and to society. Currently, there are few effective treatment options available for patients with spinal cord injuries, although there are a few promising indications that physical therapy or chronic intermittent hypoxia (CIH), may have beneficial effects. Exposure to intermittent hypoxic episodes has been shown to initiate spinal protein synthesis. However, studies have also shown that chronic intermittent hypoxia has other drawbacks as a treatment for spinal cord injuries. For example, certain CIH treatment methods can cause systemic hypertension, altered sympathetic chemoreflexes, and hippocampal cell death by the process of apoptosis.
Physical training and preconditioning have been used to treat SCI. Almost all patients with spinal cord injuries can now achieve a partial return of function with proper physical therapy that maintains flexibility and function of the muscles and joints, and strengthens the neural pathways that underlie movement. Physical therapy can also help reduce the risk of blood clots and boost the patient's morale. Physical training currently being investigated includes body weight-supported treadmill training, in which patients with partial spinal cord injury “walk” on a treadmill while they are partially supported through the use of a specially designed harness attached to an overhead lift. Unfortunately, this type of therapy is very expensive, and efficacy is far from complete.